The present invention relates to a method of manufacturing a crosslinking formed body having a low hardness, superior tensile characteristics, and rubber properties.
A silane water crosslinking formed body, which is obtained by the steps of graft polymerizing polyethylene, an ethylene group copolymer, such as an ethylene-vinyl acetate copolymer, an ethylene propylene rubber, and the like, or polyethylene derivatives, such as chlorinated polyethylene, and the like, with an organosilane compound in the presence of a free radical generating agent, forming a formed body of desired shape, and exposing the body to water in the presence of a silanol condensation catalyst to form a crosslinking formed body, is practically used in various fields; more particularly, a silane water crosslinking body of polyethylene is used as a cable insulator and for pipes. A silane water crosslinking body formed of a blended body of polyethylene and ethylene propylene rubber also is practically used as a flexible cable insulator.
However, the tensile strength of the silane water crosslinking body of ethylene group copolymer is lower in comparison with that of a non-crosslinking body. Particularly, the above tendency is significant with a silane water crosslinking body of the ethylene propylene copolymer. In order to prevent a decrease in the tensile strength, an inorganic reinforcing agent, such as carbon black and the like, or a crystalline polymer, such as polyethylene, have been conventionally added (JP-B-54-20235 (1979). As for the method of adding an inorganic reinforcing agent, a hygroscopic property of the reinforcing agent will cause foaming, the polymer becomes susceptible to scorching readily and the surface of the extruded formed body is roughened, and the workability of the extruding operation is decreased by burnt resin accompanied with the scorching. As for the method of adding a crystalline polymer, the hardness is increased, and the rubber properties, such as a permanent set of compression or elongation, are significantly decreased.